Delete OCR from PDF

See the pdfseparate and pdfunite commands from poppler-utils. The first to separate the pages from each document into individual files, and the second to merge them in the order you want in a new document.

Also note that since scanners give you raster images anyway (which some like yours can concatenate into a PDF files), maybe you can configure it to output images (png, tiff...) instead, and do the concatenation into a PDF yourself with ImageMagick.

Here is how I would remove the OCR-ed text should I have to...

First, you need to know, that OCR-ed text in a PDF is not a layer, but a special text rendering mode. The following screenshot from the official PDF specification lists all available text rendering modes:

For more background, please see these answers of mine on StackOverflow:

• "How can we make the invisible text visible?"
• "Creating 'text' in OCR-ed PDF"

Now for the procedure I envisage:

0. Make a backup of your original PDF file

'nuff said...

1. Use qpdf to un-compress most of the PDF objects

qpdf is a beautiful command line tool to transform most PDFs into a form that makes it easier to manipulate through a text editor (or through sed):

qpdf                       \
  --qdf                    \
  --object-streams=disable \
    input.pdf              \
    editable.pdf

2. Search for spots where PDF code contains 3 Tr

All spots in the editable.pdf where there is 'invisible' (a.k.a. neither filled nor stroked) text is marked by an initial definition of

3 Tr

Change these to now read

1 Tr

This should make the previously hidden text visible. Glyphs will appear in thick outlines, overlaying the original scanned page images.

It will look very ugly.

Save the edited PDF.

3. Change Tj and TJ text stroking operators to 'no-ops'

Whenever a text string is prepared for being rendered, the actual operator that is responsible for doing so is named Tj or TJ.

Look out for all of these. Replace them by tJ and tj. This will change them into 'no-ops': they have no meaning at all in the PDF source code; no PDF viewer or processor will "understand" them. (Be careful not to change the number of bytes when replacing stuff in PDF source code, because otherwise you may cause it to become "corrupted".)

Save the PDF file.

4. Check how the PDF file looks now

The PDF should now look "clean" again. The renamed text operators do not have any meaning any more for the PDF viewer, nor for any PDF interpreter.

5. Use Ghostscript to create the final PDF

This command should achieve what you want:

gs                        \
  -o final.pdf            \
  -sDEVICE=pdfwrite       \
  -dPDFSETTINGS=/prepress \
   editable.pdf

This final step uses editable.pdf as input. It outputs final.pdf. The output will have removed all traces of text. The input still had the text, albeit in an "unusable" form, because the operator renaming. Since Ghostscript does not "understand" the re-named operators, it will simply skip them by default.